Rapid detection of sludge moisture content based on the frequency domain reflection

The moisture content (MC) of sludge is a critical factor affecting sludge treatment and disposal technologies. Traditional drying methods for measuring sludge MC are time-consuming and lack of portability. To achieve rapid online detection of sludge MC, this paper proposes a method based on frequency domain reflectometry. The theoretical feasibility of detecting MC using the frequency reflection principle was demonstrated. The model of the relationship between MC and dielectric constant, as well as the relationship between dielectric constant and oscillation frequency, was derived. The mathematical model correlating MC of sludge with oscillation frequency was established, and the structure of the sensor probe was designed. Experimental results show that the third-degree fitting curve achieving the best <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>R</mml:mi><mml:mi>t</mml:mi><mml:mn>2</mml:mn></mml:msubsup></mml:math> of 0.98247. The proposed method presents good measurement performance compared to the drying method, with satisfactory repeatability and consistency in performance tests. For the sludge samples with MC ranging from 10% to 75%, the maximum error is 3.4%, and the average absolute error is 1.86%. This method provides an effective way for rapid detection of sludge MC, offering shorter measurement times and better portability compared to traditional methods.